Field of the Invention
Embodiments of the present application relates to the art of a control system for a hybrid vehicle in which a prime mover includes an engine and a motor, and especially to a control system for a hybrid vehicle to shift an operating mode between an engine mode and a motor mode.
Discussion of the Related Art
JP-A-2013-189047 describes a control system for a hybrid vehicle having an engine and two motors. In the hybrid vehicle taught by JP-A-2013-189047, an operating mode can be selected from hybrid mode (to be abbreviated as “HV mode” hereinafter) in which the hybrid vehicle is powered by the engine, single-motor mode in which the hybrid vehicle is powered by any one of the motors, and dual-motor mode in which the hybrid vehicle is powered by both of the motors. According to the teachings of JP-A-2013-189047, when the operating mode is shifted from the single-motor mode or the dual-motor mode to the HV mode, the engine is started by any one of the motors. However, if the motor generating power for propelling the vehicle is used to start the engine, shocks may be caused by a reduction in driving force when shifting the operating mode from the dual-motor mode to the HV mode. In order to prevent such reduction in driving force, the control system taught by JP-A-2013-189047 is configured to switch the operating mode at a timing when a required driving force is decreased to a level possible to propel the vehicle by only one of the motors even if the other motor is used to carry out a cranking of the vehicle.
That is, the operating mode of the hybrid vehicle taught by JP-A-2013-189047 can be selected from the mode in which the vehicle is powered mainly by the engine to ensure comparatively great driving force, and the mode in which the vehicle is powered mainly by electric power(s) of the motor(s). According to the teachings of JP-A-2013-189047, selection of the operating mode is made based on a required driving force and a state of charge of a battery. However, in a hybrid vehicle provided with a mode selecting switch, the operating mode can be switched manually. In this case, if a switching operation to the HV mode is executed under conditions that the state of charge of the battery is low and that the required driving force is large, the above-explained reduction in the driving force may be caused by starting the engine using the motor generating the driving force. In addition, a reaction force to start the engine is applied to driving wheels. Consequently, reduction in acceleration and shocks would be caused.